Accelerometer



March 16, 1954i P. J. CHENERY ACCELEROMETER Filed Dec. l5, 1948IIIIIIIIIIII v 4 gggui Patented Mar. 16, 1954 UNITED STATES PATENTOFFICE AccELERoMETER Peter J. Chenery, Pelham, N. Y., assigner to TheSperry Corporation, a corporation of Delaware Application December 15,1948, Serial No. 65,405

2 Claims.

This invention relates to accelerometer devices for detecting tilt abouta horizontal axis from a reference position.

The device includes a gravitationally sensitive part that ispositionable, relative to a part movable about a horizontal axis, by aparticular component of g to determine the reference position of themovable part. Sensitivity as to the direction of tilt of the movablepart from the reference position is obtained by arranging the parts sothat the effective component of g en the sensitive part becomes eithergreate-r than or less than the component of g determining the referenceposition when tilt occurs. While the vertical directivity of theacceleration of gravity provides the actual reference for the device,the sensitive part provided in accordance with the present invention isarranged in relation to the vertical directivity of g so that it ispositioned by a cornponent of g such as g times the cosine 45 todetermine the reference position of the sensitive part to the part withwhich it is compared.

One of the features of the invention resides in the provision of adevice of this character having a sensitive mass or weight responsive tothe acceleration of gravity that is positionable to detect tilt from ahorizontal reference attitude approximating a level condition.

A further feature of the invention resides in the combination of adevice of this character in a dirigible craft to provide a singleelement for controlling the craft automatically about one of itshorizontal axes operable in an automatic pilot, the arrangement of thedevice in the craft being such as to obtain a response therefrom toaccelerations of the craft in the vertical plane, to :D

angular accelerations of the craft about the horizontal axis of thecraft about which it is effective to exert control` and to tilt in theattitude of the craft from a reference position about such axis.

The device is fixed to the craft and arranged so that the sensitiveelement responds in a proper sense regardless of the fact that the craftmay be subject to any combination of the above noted conditions.

I Otherfeatures and structural details of the invention will be apparentfrom the following description when read in relation to the accompanyingdrawing, wherein Fig. 1 is a side elevation of a device constructed I inaccordance with the present invention with the frame or housing partthereof in vertical section. This figure also includes a schematicshowing a circuit arrangement for an aircraft automatic pilot in whichthe device functions as 2 the single control element in connection witha suitable pick-off.

Fig. 2 is a perspective view of a dirigible craft showing the locationand arrangement of the acceleration responsive device therein.

With reference to the drawing, a device embodying the present inventiveconcepts is shown to include a frame or first part I0 in the form of ahousing. The frame IS is xedly connected in a suitable manner to a bodyII such as that of a dirigible craft as shown in Fig. 2. The frame I) istherefore mounted on an object that is movable about a horizontal axiswhich may be considered for example the pitch axis of the craftillustrated. As shown in Fig. 2, the roll or fore and aft axis of thecraft is indicated at I2. The vertical or yaw axis of the craft isdesignated at I3. The pitch axis I4 of the craft is perpendicular toboth axes l2 and I3 and extends through the crafts center of gravity I4. Motion about the pitch axis is controlled by means such as theelevators I5. As shown, in Fig. 2 the tilt detecting device is mountedon the dirigible craft II forward of its pitch axis I4 and below itsroll or fore and aft axis l2. The frame l0 of the device is fixed to theobject on which it is used so that it moves with movement of objectabout its pitch or horizontal axis.

The sensitive or movable part of the device is shown in Fig. l in theform of a spring restrained mass or Weight I6. Part It of the device ispositionable by a reference defining component of g, the acceleration ofgravity, relative to the rst part or frame I0 along a path at an acuteangle tothe vertical in a plane normal to the axis I4 provided for thedevi-ce. The Weight may be supported as shown by two leaf springs I lwhich connect the same to the frame or first part it). The accelerationof gravity is indicated bya vector designated by the arrow I8 in thedrawing. The frame l as shown in Fig, l is illustrated in a positioncorresponding to a level condition of the object or craft about axis I4.At this time, the mass Iii is situated in a reference dening positionrelative to the frame along a path at a 45 degree angle to the verticalas indicated by angle A in Fig. l. The path along which the mass ismovable relative to the frame is indicated byline 2t.

Means for damping the movements of the part It may be provided as shownin the form of an electromagnetic device having a vane 2| connected tothe mass. The vane 2l is situated in the magnetic field of a magneticelement 22 xedly mounted on the frame I0 in a suitable manner.

The reference position of the craft or object about axis I4 isconsidered one in which the pitch attitude is such that the craft isneither climbing, or moving in a positive sense relative to thereference position, or diving, or moving in a negative sense relative tothe reference position. In accordance with the invention the parts ofthe device are so arranged that mass I6 is positionable relative sto theframe I0 by a particular component of g, in this instance g cosine 45,to determine the reference position of the frame. The mass I6 is alsopositionable by a component of g with tilt of the frame that is eithergreater than or less than the component of g determining the referenceposition. In the operation of the device inFig. 1, with :tilt of theframe in a positive sense, that is, when the nose of the craft rises,the frame moves in a clockwise direction as viewed in this figure sothat the angle between line 20 and vector I8 becomes 4smaller such asindicated by `angle B. With tilt in a negative sense, that is, :when thenose of the craft goes down, the Vf rame moves inga counterclpckwisedirection `as viewed in this figure so that the angle between line 20and vector I8 becomes larger 4such as indicated by angle ;C. Tilt is-thus detected by the device by an increase in the effective componentof g with tilt in a positive sense `so that the mass moves downwardlyrelative to the frame. a negative sense, 'as the component of gon themass I6 decreases, the mass moves upwardly relative `to the frame. Inother words, the parts of the device are so arranged that with tilt ofthe frame the angle A either initially increases or decreases inaccordance with the sense of tilt of the frame from its referenceposition. In the illustrated embodiment of `the invention, the deviceoperates ywithin an effective range Voi ninety degrees, the frame beingvtiltable from a level condition about a horizontal a-xis in a positivesense through forty-five degrees and in a negative sense throughforty-five degrees. At the effective upper limit of forty-five degreepositive tilt, the effect of gravitational acceleration .i

on the mass IE is one g. At the effective `lower limit of forty-fivedegree negative tilt, the effect of gravitational acceleration is null.When the frame is in a level condition, the mass is positioned relative-to the frame, by the effect thereon 5;.

of a component of gravitational acceleration between one g and nullwhich in the arrangement shown is a cosine forty-five degree componentof g. The device is useful in combination with an `indicator to `measuretilt and in combination rfi with a steering means to correct tilt.

Indicating means for the device `may `be provided by a suitablephasesensitive galvanometer -23 that is operated by the output of a pick-off24 by way of leads 25, 26. The pick-off illustrated is an E-transformertype signal device whose ,stator is fixed to the frame I0 and whosearmature is connected to move with the mass IB. rIhe central leg of thestator of the pick-off isenergized by a vsuitable source of alternatingcurrent electrical energy. The output windings of the pick-off connectwith leads 25 and 26. With the armature in a central position relativeto the stator, the output signal from the pick-off is null so that thepointer of the galvanometer fi indicates a condition of zero pitch forthe craft. The piek-off reflects the relative movements of the mass I6Arand frame I0 from the reference position, the same providing a signalfor operating meter v23 whose amplitude depends on the with tnt inextent of the relative displacement of its armature and stator and whosephase depends on the sense of the displacement. Since the sensitive massI6 is secured between and fiat against the end portions of the pair ofsprings I1 which extend in parallel relation from opposite walls of theframe II) as shown in Fig. l, movement of said mass in response toacceleration components acting on the` mass in ,a direction normal tothe fiat surfaces of 'the springsfwill be Vsubstantially linear.Therefore, if one part of pick-off 24 is scoured to the mass and theother part thereof `is ,secured to the frame, relative movement betweenthe two parts will be substantially linear and wilLitherefore 'providean output signal on lleads 25 Iand F26 which varies substantiallylinearly with, the 44effective component of acceleration acting on themass.

:As ishown, the tilt `detecting device may be employed in combinationwith a dirigible craft having an automatic :pilot for controlling thecraft about a horizontal Vaxis such yas axis M. In this instance, thepick-off A:24 of the device provides the soie control signal for .anautomatic pilot that is shown `operatively connected to the elevators I5of the craft I I. .As illustratively shown in Fig. ,1, such an`automatic Pilat may include a servo "amplifier 2.1 adapted to receivethe output of the pick-off 214. The 'output of amplifier 21 may be fedto the ,field :circuit `of a ldirect current generator ,28.91:fmQtQr-.Eeneb ator s et of the Ward-Leonard type. `las fshovm, thearmature circuit .of 4generator .2.8 renergm the armature of aA,servornotor 219,. Theseld cb;- cuit (not shown) of motor '29 iS:energized .from aoonstant source. Generator 28 is driven'bya constantspeed motor 30 that is lenergized*frmn a constant source. lTheservomotor ^29 iis meera-` tivel-y connected to the elevators I5 ofthegcraft by way of suitable reduction gearing, @a cable drum 31 andcable 32., The ,automatic pilotunay include a position repeat-back in.the form of s. selsyn device `33 whose rotor is positioned inaccordancewith the `displacement of .elevators .Il from a null condition toprovide a .feed-aback sig.- nal for the automatic pilot. As shown,isuchsa signal may 'be fed tothe amplifier 2I by'wayofV 2. This axis asshown may be -the pitchaxis I4 .of

the craft. `'I'he mass I6 of the device correctly senses upwardverticalacceleration, `positive angular acceleration `and a V'nose `upteonditiqn 01 the craft-to cause ,pics-01H4'toproduceasisml to operatemotor 29 to move the elevators t! downwardly. VThe opposite result .isobtained when the `mass I6 senses negative angular accaleration about,axis I4, downward rvertical.:accali eration and a nose down Aconditionof thecraft. While the device cannot ,distinguish between theaccelerations that it responds to, the `device provides proper sensing`for each Within a v,limited range to obtain necessary correction. The.device provides proper .sensing within a ranger! 1 /4.5 .degrees from.a level .condition which `defina its effective limits of operation. Aswitch 36 may be provided to disable the automatic pilot if the craft isto be acrobatically maneuvered. Close regulation of the craft isobtained by an automatic pilot including the described sensing devicewithout the need of rate signals in the system such as ordinarilyrequired where a gyroscopic reference device is employed.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An accelerometer of the character described comprising a frame, apair of flat, leaf springs each having one end thereof secured toopposite walls of said frame and the other end thereof extending insubstantially parallel relation from said opposite walls, said springsbeing of such length that the end portions thereof lie in relativelyspaced overlapping positions, a mass secured between and hat against thesaid end portions of both springs, the thickness of said springs beingsuch that flexing thereof occurs upon movement of said mass in responseto acceleration components acting on said mass in a direction normal tothe broad hat surfaces of the springs and the width of said springsbeing such as to rigidly resist flexing thereof in response toacceleration components acting on said mass in a direction edgewise ofsaid springs, and a two part pick-off having one part secured to saidmass and the other part secured to said frame, whereby linear motion ofsaid mass will occur displacing the one part of said pick-off linearlywith respect to the other part thereof to thereby provide an outputsignal which `varies linearly with the effective acceleration componentacting on said mass.

Aif)

' extending in substantially parallel relation from said opposite walls,said springs being of such length that the end portions thereof lie inrelatively spaced overlapping positions, a mass secured between and flatagainst the said end portions of both springs, the thickness of said,springs being such that flexing thereof occurs upon movement of saidmass in response to acceleration components acting on said mass in adirection normal to the broad flat surfaces of the springs and the widthof said springs being such as to rigidly resist exing thereof inresponse to acceleration components acting on said mass in a directionedgewise of said springs, and an E-type pick-off having its coresupported by said frame and its armature secured to said mass, wherebylinear motion of said mass will occur displacing said armature linearlyrelative to said core thereby providing an output signal which varieslinearly with the eifective acceleration component acting on said mass.

PETER J. CHENERY.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,154,396 Hayot Sept. 21, 1915 1,959,804 Wittkuhns et al. May22, 1934 2,125,361 Schwarzler Aug. 2, 1938 2,139,558 Moseley et al Dec.6, 1938 2,302,670 Buchanan Nov. 24, 1942 2,317,028 Chappell et al Apr.20, 1943 2,386,777 Bentley Oct. 16, 1945 2,487,793 Esval et al. Dec. 18,1946 2,498,997 McLean Oct. 27, 1948

